Caracterização química e mineralógica de amostras dos corpos minerais majoritários de uma mina subterrânea de minério de ouro e sua influência na recuperação do metal precioso

Abstract

Gold ore processing has become increasingly challenging due to the exhaustion of higher grade deposits and increasing complexity of metal recovery. In this context, characterization is a fundamental step within the geometallurgy approach, as it provides the mineralogical knowledge necessary for the correct definition of process routes and allows the optimization of the overall yield of a metallurgical plant. The objective of this research was to characterize the three major ore bodies (BF, BF2 and LPA) of the Pilar mine of Jaguar Mining Inc., a Brazilian company with foreign capital, which produces gold in the Iron Quadrangle. The methodology involved the integration of information provided by chemical analyses, mineral characterization by SEM-EDS/MLA (Mineral Liberation Analyser) and X-ray diffractometry, and laboratory tests of metallurgical concentration (gravimetry, flotation and leaching), in order to determine the mineralogical associations and to understand the behavior of each one of these bodies in the hydrometallurgical process. The characterization results showed that there is a difference in the composition of mineral phases in these bodies, with quartz being one of the most abundant mineral and common to all; the other minerals differ in terms of concentration in the bodies, the main ones for BF being chlorite, muscovite and ankerite; for BF2, siderite and stilpnomelane; and for LPA, siderite and arsenopyrite. The concentration of sulfides does not exceed 16.00 %, and the majority are arsenopyrite and pyrrhotite. The gold grains identified were mostly native gold, included in arsenopyrite and with an average diameter of less than 0.010 mm. The metallurgical tests indicated that none ore body was considered refractory. The yield was more than 70.00 % of gravity gold and recovery by direct cyanidation followed by adsorption above 91.00 % in the granulometry of 80.00 % of particles below 0.075 mm. In the flotation stage, the recoveries and tailings contents were quite different between the applied conditions and bodies, with the BF body having the worst performance. The combination of reagents based on dithiophosphates and xanthates has promoted better performance in the gold recovery in flotation, but the inclusion of the flotation step for the gravity tailings, followed by cyanidation/adsorption of the flotation concentrate, resulted in a reduction in the global recovery of gold by up to 8.88% compared to direct cyanidation recovery. The circuit with the best metallurgical recovery results for all ore bodies was gravity and cyanidation of the gravitational tailings. The results indicated that the knowledge of the mineralogical characteristics of each ore body, associated with specific process conditions for gravity, flotation and leaching, can increase the gold extraction efficiency and minimize losses.